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| Monolithic collapse of a weakly magnetized cloud to form black holes |
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Image Credit: Cai and Shu
Monolithic collapse of a weakly magnetized cloud to form black holes. The red circle indicates the expansion wave, and the blue curves are the magnetic field lines. The left panel shows a black hole formation, and the right panel shows the Newtonian limit
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| The concept of inside-out gravitational collapse can be naturally extended to black hole formation. Initially the inward pull of gravity is balanced by the pressure gradient in the gas cloud. As the central piece of the cloud collapses to within its gravitational radius, the layer immediately above loses pressure support, and starts to fall toward the incipient black hole, which triggers the next layer to fall. The information of gravitational instability propagates outward at the speed of sound in the form of an expansion wave, and the entire cloud collapses layer by layer. In the figure, the expansion wave is represented by the red circle, and the growing black hole is represented by the black filled circle at the center. Outside of the expansion wave, gas remains in local hydrostatic equilibrium. If the original gas cloud was threaded by a uniform but weak magnetic field (represented by the blue curves), then the subsequent evolution would arrange the field lines in the form of a split magnetic monopole at the center. Since an outside observer would never see matter crossing the event horizon, the magnetic field lines appear as a toupee pasted onto the black hole. |
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